It wouldn't have to. 10k years ago, the sea level was way lower. At the end of the ice age, the sea rose by about 100m. The Dover strait was dry land during the

It wouldn't have to. 10k years ago, the sea level was way lower. At the end of the ice age, the sea rose by about 100m. The Dover strait was dry land during the ice age. So if those places were built long enough ago, they would have been over the sea level.